1. Field of the Invention
The present invention relates to a thin film magnetic head in which a coil layer is formed between core layers and, in particular, to a thin film magnetic head capable of achieving a reduction in coil resistance value without involving a deterioration in magnetic efficiency.
2. Description of the Related Art
An inductive head for recording a recording signal on a recording medium provided, for example, in a hard disk apparatus, comprises lower and upper core layers of a magnetic material and a coil layer formed between the core layers.
A base portion of the upper core layer is magnetically connected to the lower core layer. In the plane (ABS plane) opposed to the recording medium, a magnetic gap is formed between the lower and upper core layers.
The coil layer is wound around the base portion of the upper core layer, and the conductor width of the coil layer in each turn is substantially the same. When a recording current is supplied to the coil layer, a recording magnetic field is induced in both core layers, and due to a leakage magnetic field from the magnetic gap portion, a magnetic signal is recorded on a recording medium such as a hard disk.
However, the coil length of the coil layer in each turn is longer on the outer side than on the inner side, so that when the conductor width in each turn is substantially the same as in the conventional art, the coil resistance value rapidly increases in a turn on the outer side, and the coil resistance value of the entire coil layer increases, making it impossible to effectively cope with the recent tendency to record in high density.
To solve the above problem, Japanese Patent Laid-Open No. 7-57217 discloses an example in which, as shown in FIG. 1, the conductor width of the coil layer formed on the rear side with respect to the base portion of the upper core layer (on the opposite side with respect to the side opposed to the recording medium) is formed so as to become gradually larger from the inner side to the outer side of the coil layer. According to this publication, by making the conductor width on the rear side with respect to the base portion of the upper core layer gradually larger, it is possible to restrain the coil resistance value of the turn on the outer periphery where the coil length is large, making it possible to reduce the coil resistance value of the entire coil layer.
Further, according to this publication, it is desirable as in the prior art to make the conductor width of each turn on the front side with respect to the base portion of the upper core layer (the side opposed to the recording medium) the same dimension. This is for the reason that the coil layer formed on the front side with respect to the base portion must be formed between the base portion of the upper core layer and the forward end portion. If the conductor width of each turn on the front side with respect to the base end portion is larger than in the prior art, it is necessary to make the length between the base end portion and the forward end portion of the upper core layer large, so that the magnetic path length formed from the lower core layer to the upper core layer becomes rather large, resulting in a deterioration in magnetic efficiency.
However, if the conductor width of each turn formed on the front side with respect to the base end portion of the upper core layer is of the same dimension as in the prior art, the coil resistance value of each turn on the front side with respect to the base end portion rapidly increases from the inner to the outer side, so that there is a fear that the coil resistance value of the entire coil layer cannot be effectively reduced.
Further, at page 3, column 0014, lines 4 through 6 of this publication, there is a description to the effect that xe2x80x9cit is possible to adopt a configuration such that the line width, including the front side, gradually increases from the inner to the outer sidexe2x80x9d. However, if the conductor width of the coil layer on the front side with respect to the base end portion of the upper core layer is made gradually larger from the inner to the outer side without any restriction, the conductor width of the entire coil layer on the front side with respect to the base end portion increases, so that it is necessary to increase the length between the base end portion and the forward end portion of the upper core layer, with the result that the magnetic path length increases, which leads to a deterioration in magnetic efficiency.
The present invention has been made with a view toward solving the above problems. Accordingly, it is an object of the present invention to provide a thin film magnetic head capable of correcting the configuration of the coil layer and effectively reducing the coil resistance value without involving a deterioration in magnetic efficiency.
In accordance with the present invention, there is provided a thin film magnetic head comprising a lower core layer formed of a magnetic material, an upper core layer of a magnetic material forming a magnetic gap between it and the lower core layer at a portion opposed to a recording medium, and a coil layer which is formed in a pattern so as to be wound around the periphery of a base end portion of the upper core layer and which induces a recording magnetic field in the lower core layer and the upper core layer,
wherein the conductor width of the coil layer when a first normal extending from the center of the coil layer toward the outer periphery of the coil layer is measured increases from the inner to the outer side in at a fixed ratio, and wherein the conductor width of the coil layer in each turn is such that the conductor width on the first normal extending from the center of the coil layer to the side opposed to the recording medium is smaller than the conductor width on a second normal extending from said center in a direction opposite to the first normal.
As described above, in the present invention, the conductor width of the coil layer when the normal extending from the center of the coil layer toward the outer periphery of the coil layer increases at a fixed ratio from the inner to the outer side. In particular, in the present invention, the conductor width of the coil layer formed on the side opposed to the recording medium with respect to the base end portion of the upper core layer also increases at a fixed ratio from the inner to the outer side, so that the coil resistance value of the coil layer formed on the side opposed to the recording medium with respect to the base end portion is not extremely large. Due to the above arrangement, in the present invention, it is possible to restrain an increase in the coil resistance value in each turn from the inner to the outer side or reduce it, and it is possible to reduce the resistance value of the entire coil layer as compared with the prior art. Further, by increasing the conductor width at a fixed ratio, it is possible to set the increase or decrease in the coil resistance value in each turn from the inner to the outer side to a substantially fixed value, so that it is possible to set the coil resistance value of the entire coil layer within a fixed range beforehand, making it possible to form the coil layer in a pattern.
Furthermore, in the present invention, the conductor width on the first normal extending from the center of the coil layer to the side opposed to the recording medium is smaller than the conductor width on the second normal extending from said center in a direction opposite to the first normal, whereby there is substantially no need to make the length between the base end portion and the forward end portion of the upper core layer larger than in the prior art. Thus, in the present invention, the length of the magnetic path formed between the upper core layer and the lower core layer is not large, and it is possible to make the magnetic efficiency approximately the same as in the prior art or increase it as compared to prior art.
Further, in the present invention, the coil layer is wound in not less than 5 turns, and assuming that the coil resistance value of the one turn positioned on the outermost side of the coil layer is DCRout, and that the coil resistance value of the one turn positioned nearest to the center of the coil layer is DCRin, the percentage of DCRout/DCRin is approximately not less than 45% and not more than 230%.
As described above, in the present invention, the conductor width increases at a fixed ratio from the inner to the outer side of the coil layer. In addition to that, the coil layer is formed in a pattern such that the coil resistance value of the coil layer in the innermost turn and that in the outermost turn are in the above range, whereby it is possible to reduce the coil resistance value of the entire coil layer as compared with the prior art, in which the conductor width of the coil layer is substantially the same in the inner and the outer side.
Further, in the present invention, it is desirable that the coil resistance value of one turn is substantially the same value in each turn. In this way, by forming the coil layer in a pattern such that the coil resistance value of each turn is substantially the same, it is possible to reduce the resistance value of the entire coil layer more effectively, as clarified by the results of an experiment described below.
Further, in the present invention, it is desirable that the conductor width of the coil layer in each turn be constant in a predetermined range including the first normal, whereby it is possible to make magnetic path length substantially the same as in the prior art or shorter than in the prior art, making it also possible to make the magnetic efficiency substantially the same as in the prior art or increase it as compared with the prior art.
Further, in the present invention, it is desirable that the conductor width of the coil layer in each turn be constant in a predetermined range including the second normal, the conductor width of the coil layer in each turn be the largest on the second normal and gradually decrease toward both sides, whereby it is possible to reduce the coil resistance value of the entire coil layer.
Further, in the present invention, it is more desirable that the conductor width increase ratio be set such that the coil resistance value of each turn is substantially the same from the inner to the outer side of the coil layer. When the coil resistance value of each turn is substantially the same value, it is possible to reduce the coil resistance value of the entire coil layer most effectively.